Erosion-Corrosion Behavior and Mechanism of Heated Electroless Ni–P Coating under Flow

Abstract

To study on erosion-corrosion behavior and mechanism of Ni–P coating (Ni–P) and Ni–P coating after heat treatment at 400°C (h-Ni–P) in liquid flow and solid-liquid flow, the numerical simulation, microstructure, and electrochemical methods were applied. It could be seen that the spherical structure of the coating surface was no longer dense, and the coating changed from amorphous to crystalline after heat treatment at 400°C. Numerical simulation showed that the coating possessed a higher velocity and a small static pressure at the edge in the straight pipe. The electrochemical analysis showed that the i_corr of Ni–P and h-Ni–P became larger and the R_p became smaller as the solution speed increased, the i_corr of h-Ni–P was larger than that of Ni–P, the R_p of Ni–P was larger than that of h-Ni–P. In addition, the both coating had a higher i_corr in the solid-liquid flow than that of the liquid flow at the same speed. The results indicated that the corrosion resistance of Ni–P coating was reduced because it had become the crystal after heat treatment at 400°C. The numerical simulation was helpful to reveal the local stress information of Ni–P coating under flow.

The electroless Ni–P coating was prepared on the substrate of Q235 steel. Then the erosion-corrosion behavior and mechanism of Ni–P coating (Ni–P) and that heated at 400°C (h-Ni–P) in the flow were studied by numerical simulation, electrochemical and microstructure method. The study will provide a referential significance for the erosion-corrosion behavior and mechanism of Ni–P coating.